The hypothesis of this project is that liquid enteral feeding supplements significantly affect the measurement of gastric intramucosal carbon dioxide levels (PgCO2) in normal healthy volunteers. The specific aim is to evaluate whether enteral feeding can be given into the stomach lumen via a gastric tonometer without significantly affecting the measurement of gastric regional CO2 levels. This is a pilot study to examine the effect of gastric enteral feeding on tonometrically measured PgCO2 in healthy volunteers. An air tonometry system will be utilized to monitor PgCO2 levels by a tonometer placed in the lumen of the stomach via nasogastric intubation. PgCO2 levels will be automatically monitored and recorded every 15 minutes throughout the study. Osmolite High Nitrogen (HN) will be utilized for enteral feeding. It has been well documented that the gastric tonometer is a useful tool in measurement of PgCO2 levels. Studies have demonstrated significant increases in PgCO2 with induction of endotoxemia and occlusion of the mesenteric vasculature, thus establishing the use of PgCO2 as an accurate indicator of splanchnic perfusion. PgCO2 has also been shown to be a useful guide to hemodynamic management of the critically ill. In vitro studies have demonstrated that PgCO2 can be utilized as a therapeutic index of tissue oxygenation, as a prognostic value for severity of illness, and as an index for the use of dobutamine in septic patients. However, the effect of enteral nutrition on the accuracy of tonometrically measured PgCO2 has not been studied systematically. The need to answer this question regarding the effect of enteral feeding on tonometered PgCO2 levels lies in the importance of accurately assessing the critically ill patient's hemodynamic stability related to splanchnic perfusion and ability to tolerate enteral feeding. After the effect of enteral feeding on the PgOC2 levels is established in normal volunteers, future studies will be conducted on critically ill patients. Once the effect of enteral feeding on tonometered PgCO2 is established for normal and critically ill subjects, the last study will attempt to utilize the measurement of PgCO2 to intiate early enteral feeding in the critically ill patient.